Work this past year has increased our knowledge of immune response in chickens to natural substances (S. pullorum and Human Serum Albumin) and to certain synthetic compounds (GAT10, (T,G)-A-L and DNP) and substantiates that the level of response is under the control of the B locus. Further, our studies show a strong influence of the B locus on mortality from general causes as well as specific causes (Marek's Disease Virus). We thus find that the B locus major histocompatibility system in chickens follows closely the pattern of immune response and the H-2 model in mice. This past year we have made considerable progress in identifying B alleles in 7 inbred lines making them potentially more useful for future studies on immune response and disease. In general, we think our work is of significance to the overall field of immunogenetics by differences and similarities compared to other species including the H-2 in mice and the HL-A in humans.